Examples of progress made during the prior year are summarized below. 1) Building on prior work, we found increased translocator protein (TSPO), a putative biomarker of neuroinflammation, in patients with temporal lobe epilepsy (TLE) extending beyond the seizure focus and involving bilateral regions (Dickstein et al, submitted). This work was performed under clinical protocol #08-M-0158, with corresponding NCT#00696371. Neuroinflammation is thought to play a pathogenic role in several psychiatric and neurological disordersincluding Alzheimers disease, epilepsy, and strokebut the timing of inflammatory brain changes that occur during disease progression is unknown. Our laboratory has been working to identify putative biomarkers of inflammatory changes in brain in order to explore the nature of these changes. Both animal studies and clinical observations have suggested that epilepsy is associated with inflammation. A previous study from our laboratory found that in vivo expression of TSPO was increased ipsilateral to the seizure focus in 16 patients with unilateral TLE and 30 healthy subjects. We found that brain uptake was higher ipsilateral, relative to contralateral, to the seizure focus in hippocampus, parahippocampal gyrus, and amygdala (Hirvonen et al, J Nucl Med 53: 234-240, 2012). As a follow-up to this study in a larger group of patients, we recently found increased TSPO in TLE patients extending beyond the seizure focus and involving bilateral regions (Dickstein et al., submitted). By using an automated brain segmentation procedure, we obviated observer bias inherent in the manual segmentation used in our prior study, and reduced potential spillover from the choroid plexus to adjacent regions. We detected relative TSPO binding increases with 11CDPA713, a pyrazalopyrimidineacetamide ligand, in addition to PBR28, an aryloxyanilide ligand. We also replicated our prior finding of relatively increased ipsilateral 11CPBR28 brain uptake in a larger sample of TLE patients and found even greater increases with 11CDPA713. Taken together, the data show that TSPO asymmetry in TLE patients is a robust finding, independent of segmentation procedure and radioligand chemical class. 2) We built on previous work seeking to quantify the binding of 11C-(R)-rolipram, a phosphodiesterase type IV (PDE4) inhibitor as an indirect measure of this with healthy controls, and found that two months of treatment with an SSRI increased (normalized) PDE4 binding. This work was performed under clinical protocol #06-M-0215, with corresponding NCT#00369798.enzymes activity in the brain of individuals with major depressive disorder (MDD) compared PDE4, an important component of the cyclic adenosine monophosphate (cAMP) cascade, selectively metabolizes cAMP in the brain to the inactive monophosphate. Studies suggest that PDE4 mediates the effects of several antidepressants. Prior work from our laboratory confirmed in animals that increased 11C(R)-rolipram binding reflects the phosphorylated / active state of PDE4. Using this radioligand, we next found that PDE4 binding is decreased in unmedicated patients with MDD, consistent with the cAMP theory of depression. To quantify the binding of 11C-(R)-rolipram as an indirect measure of this enzymes activity in the brain of individuals with MDD, we performed 11C-(R)-rolipram brain PET scans in 28 moderately depressed MDD subjects and 25 age- and gender-matched healthy controls; roughly half of patients were treatment-naive. We found that brain levels of PDE4 were decreased in unmedicated individuals with MDD in vivo (Fujita, et al. Biol Psychiatry 72: 548-554, 2012). Building on this work, and in collaboration with Dr. Carlos Zarate, we sought to determine if antidepressant treatment upregulates PDE4 in humans as it does in animals. In addition to the rolipram PET scans without medication reported above, 22 of the 43 unmedicated MDD patients had a follow up rolipram scan after starting treatment with SSRIs. In this ongoing study, our pre-determined sample size is 25 patients to be scanned after SSRI treatment. These patients showed an increase of 13 36% in rolipram binding after SSRI treatment across all brain regions (p = 0.001 when age was used as a covariate). In contrast, 11 healthy controls who had a repeat scan without SSRI showed similar binding on repeat scans with changes of only -2 13%. The change in rolipram binding after SSRI varied markedly among patients as indicated by the large standard deviation of 36%. Those patients with lower rolipram binding before SSRI showed significantly greater increases after therapy (p < 0.007 in all regions) indicating normalization of rolipram binding by treatment. Older patients also showed greater increases in rolipram binding after SSRI (p &#8804; 0.001) while young patients with higher baseline rolipram binding tended to show decreased rolipram binding after SSRI. According to the interim analysis in July 2014, the changes in rolipram binding did not correlate with symptom improvement in all patients. Nevertheless, posthoc analyses after the full sample size has been accrued (i.e., 25 patients) may show correlations in subgroups of patients and/or specific regions of brain. Taken together, these results elucidate two important and related points. First, the cAMP cascade, as indirectly measured with PDE4 binding, was downregulated in unmedicated patients with MDD. Second, antidepressant treatment normalized this 11C(R)-rolipram downregulation. These studies suggest that PDE4 inhibition, perhaps via subtype selective agents, might again be assessed for efficacy in MDD; the results also broadly support the cAMP theory of depression and of antidepressant action.